coastal landforms Flashcards
how do waves form?
- wind blowing over sea
- friction with surface of water causes ripples- develop into waves
-circular orbit in open water
- friction with seabed distorts circular motion
- increasingly eliptical orbit as water becomes shallower, waves move forward
- crest of wave moves faster
- wave breaks and collapses onto beach
- water rushes up beach as swash
- water returns as backwash
constructive waves
formed by storms hundreds of kms away, common in summer
-low waves with crests far apart
- gently sloping wave front
- breaking waves push large amounts of sand and pebbles up the beach
destructive waves
formed by local storms close to the coast, common in winter
- waves close together
- waves become high, with steep wave front
- breaking waves plunge down onto beach with little forward swash
- strong backwash erodes sand and pebbles and can destroy the beach
- form a steep beach
weathering
mechanical
- freeze-thaw
- water collects in cracks in rocks
- at night, water freezes and expands, making cracks larger
- as temp rises, ice thaws and water seeps deeper into rock
- repetition makes fragments break off
chemical
- carbonation
- rainwater absorbs CO2, becomes acidic
- contact with alkaline rocks e.g. limestone, produces a chemical reaction causing rocks to dissolve
biological
- plant roots grow in cracks of rocks, and animals burrow into weak rocks
mass movement
downward sliding of weathered material/rock
rockfall
- rock breaks open due to freeze-thaw
- scree falls off cliff-face
landslide
- blocks of rock slide downhill
- detached rock collects at the bottom of a slide plane
mudflow
- saturated soil and weak rock flows downhill
rotational slip
- slump of saturated soil and weak rock along a curved surface
factors affecting development of coastal erosion landforms
-Geological structure
(arrangement of rocks and features like folding and faulting)
-Rock type
(some rocks are tougher/more resistant than others. For example, granite, limestone and chalk are harder than sand and clay)
types of coastal erosion
solution
- dissolving of soluble chemicals in rock
corrasion
- rock fragments picked up by the sea are thrown at the cliff
- scrape/wear away the rock
abrasion
- sandpapering effect of pebbles grinding across rocky platform
attrition
- rock fragments carried by sea knock against each other becoming more smaller/rounded
hydraulic power
- power of waves as they hit a cliff
- trapped air is forces into cracks in the rock causing it to break up
longshore drift
movement of sediment depends on direction of waves approaching the coast as a result of prevailing wind
- where waves approach at an angle, sediment is moved along the beach in a zig-zag pattern
How are headlands and bays formed
-Bands of rocks of different strengths in coastline
-weaker bands are eroded more rapidly
-stronger bands eroded more slowly
-eroded clay forms bays where (under sheltered conditions,) sand is deposited which forms beaches
-resistant rock sticks out to form headland
-lack of shelter means deposition does not occur- so no beaches
How are cliffs and wave-cut platforms formed?
-waves break against cliff
-erosion will wear away the cliff at high-tide line to form wave-cut notch
-notch will get deeper, undercutting the cliff
-overlaying cliff collapses
-cliff will gradually retreat
-leaving a sloping rocky platform
-which is smooth due to abrasion
How are caves, arches and stacks formed?
-fault/joint in resistant rock
-vulnerable to abrasion/hydraulic action which widen the joint to form a cave
-waves make cave larger until it cuts through the headland to make an arch
-arch base is eroded and top is weathered so roof becomes too heavy and collapses
-leaving a tall stack
-stack is eroded and collapses, leaving a stump
Beaches
-deposits of sand and shingle at the coast
-waves are constructive- strong swash, weak backwash which builds up beach
-pebble beaches- high energy environments which wash away finer sand and leave large pebbles
- pebbles come from nearby eroded cliffs or are deposited onshore by vast accumulations out at sea
Sand dunes
-embryo dunes form around deposited obstacles e.g. pieces of wood/rocks
-develop and become stabilised by vegetation to form fore dunes and tall yellow dunes
-marram grass is adapted to windy exposed conditions, has long roots to find water which bind sand together- stabilising the dunes
-rotting vegetation adds organic matter to the sand making it fertile
-back dunes colonised by a range of plants
-wind can form depressions in the sand called dune slacks in which ponds may form
Spits
narrow finger of sand/shingle jutting out into the sea from land
-longshore drift transports sand along the coast
-coastline changes shape
-spit extension grows out into the sea
-spit is exposed to changes in wind/wave direction
-end of the spit becomes curved (recurved end)
Bars
Longshore drift causes a spit to grow right across a bay, trapping a freshwater lake (lagoon) behind it
offshore bar forms further out to sea
waves approaching a gently sloping coast deposit sediment due to friction with the seabed. Build up of sediment offshore causes waves to break at some distance from the coast
